• Preheat your oven to 350°F (175°C) and line a 9x13 baking pan with parchment paper. Leave enough excess parchment paper to be able to lift the brownie blondies out of the pan when done.

Mix the Brownie Batter

• In a large mixing bowl or the bowl of your stand mixer, combine sugars and melted butter. Mix until well combined, scraping the sides of the bowl as you go. Add the vanilla extract, salt, and espresso powder and stir until evenly distributed.
  1 ½ cups butter, 2 ½ cups sugar, ½ cup light brown sugar, ½ tablespoon vanilla extract, ½ teaspoon salt, 2 teaspoon espresso powder
• Incorporate the eggs one at a time and mix until smooth again between each addition. Stir in the sifted cocoa powder until fully incorporated, then add the flour and mix just enough that the flour is mixed in thoroughly.
  5 large eggs, 1 ¼ cups unsweetened cocoa powder, 1 ¼ cups all-purpose flour

Bake the Brownie Layer

• Transfer the brownie batter into your prepared pan and bake the bottom layer for 25 minutes at 350°F (175°C).

Mix the Blondie Batter

• Clean your bowl and add the melted butter and light brown sugar. Mix until well combined, then add the vanilla extract, baking powder, and salt. Mix until smooth.
  1 cup butter, 2 cups light brown sugar, 1 tablespoon vanilla extract, 1 teaspoon baking powder, ½ teaspoon salt
• Incorporate the eggs one at a time, mixing until smooth again. Add the flour and mix until just combined.
  2 large eggs, 2 cups all-purpose flour

Assemble and Bake

• Remove the brownie layer from your oven when the 25-minute bake time is up, then spoon the blondie batter over the brownie layer. Use your spatula to spread the blondie batter to the edges of the pan. *Your brownie layer is not fully set; it may mix slightly with the blondie batter - this is OK.
• Return the pan of brownie blondies to your oven and continue baking at 350°F (175°C) for an additional 25-35 minutes. Once an inserted knife or cake tester comes out with a few crumbs or fudgy (but not raw doughy), the brownie blondies are done.
• Cool the brownie blondies in the pan on a wire cooling rack completely before using the parchment paper to lift them out to slice for serving.